Mung bean (Vigna radiata) used to be known as Phaseolus aureus Roxb. before many Phaseolus species were moved to the Vigna genus (Lambrides et al., 2006). In spite of its usual vernacular name of mung bean, Vigna radiata is a different species from Vigna mungo, which is usually called black gram or urdbean. Both species have a similar morphology (see Description below).

The mung bean (Vigna radiata (L.) R. Wilczek) is a legume cultivated for its edible seeds and sprouts across Asia. There are 3 subgroups of Vigna radiata: one is cultivated (Vigna radiata subsp. radiata), and two are wild (Vigna radiata subsp. sublobata and Vigna radiata subsp. glabra). The mung bean plant is an annual, erect or semi-erect, reaching a height of 0.15-1.25 m (FAO, 2012; Lambrides et al., 2006; Mogotsi, 2006). It is slightly hairy with a well-developed root system. Wild types tend to be prostrate while cultivated types are more erect (Lambrides et al., 2006). The stems are many-branched, sometimes twining at the tips (Mogotsi, 2006). The leaves are alternate, trifoliolate with elliptical to ovate leaflets, 5-18 cm long x 3-15 cm broad. The flowers (4-30) are papillonaceous, pale yellow or greenish in colour. The pods are long, cylindrical, hairy and pending. They contain 7 to 20 small, ellipsoid or cube-shaped seeds. The seeds are variable in colour: they are usually green, but can also be yellow, olive, brown, purplish brown or black, mottled and/or ridged. Seed colours and presence or absence of a rough layer are used to distinguish different types of mung bean (Lambrides et al., 2006; Mogotsi, 2006). Cultivated types are generally green or golden and can be shiny or dull depending on the presence of a texture layer (Lambrides et al., 2006). Golden gram, which has yellow seeds, low seed yield and pods that shatter at maturity, is often grown for forage or green manure. Green gram has bright green seeds, is more prolific and ripens more uniformly, with a lower tendency for pods to shatter. In India, two other types of mung beans exist, one with black seeds and one with brown seeds (Mogotsi, 2006). The mung bean resembles the black gram (Vigna mungo (L.)) with two main differences: the corolla of Vigna mungo is bright yellow while that of Vigna radiata is pale yellow; mung bean pods are pendulous whereas they are erect in black gram. Mung bean is slightly less hairy than black gram. Mung bean is sown on lighter soils than black gram (Göhl, 1982).

The mung bean is a major edible legume seed in Asia (India, South East-Asia and East Asia) and is also eaten in Southern Europe and in the Southern USA. The mature seeds provide an invaluable source of digestible protein for humans in places where meat is lacking or where people are mostly vegetarian (AVRDC, 2012). Mung beans are cooked fresh or dry. They can be eaten whole or made into flour, soups, porridge, snacks, bread, noodles and ice-cream. Split seeds can be transformed into dhal in the same way as black gram or lentils. Mung beans can be processed to make starch noodles (vermicelli, bean thread noodles, cellophane noodles) or soap. The sprouted seeds ("bean sprouts" in English, and incorrectly called "germes de soja" or "pousses de soja" in French) are relished raw or cooked throughout the world. The immature pods and young leaves are eaten as a vegetable (Mogotsi, 2006).

By-products of mung bean processing: mung bean bran (called chuni in India), which is the by-product of dehulling for making dhal, and the by-product of the manufacture of mung bean vermicelli.

Mung bean is sometimes grown for fodder as hay, straw or silage (Mogotsi, 2006). It is particularly valued as early forage as it outcompetes other summer growing legumes such as cowpea or velvet bean in their early stages (Lambrides et al., 2006).

The mung bean plant makes valuable green manure and can be used as a cover crop (Mogotsi, 2006).

Distribution

The mung bean is thought to have originated from the Indian subcontinent where it was domesticated as early as 1500 BC. Cultivated mung beans were introduced to southern and eastern Asia, Africa, Austronesia, the Americas and the West Indies. It is now widespread throughout the Tropics and is found from sea level up to an altitude of 1850 m in the Himalayas (Lambrides et al., 2006; Mogotsi, 2006).

The mung bean is a fast-growing, warm-season legume. It reaches maturity very quickly under tropical and subtropical conditions where optimal temperatures are about 28-30°C and always above 15°C. It can be sown during summer and autumn. It does not require large amounts of water (600-1000 mm rainfall/year) and is tolerant of drought. It is sensitive to waterlogging. High moisture at maturity tends to spoil the seeds that may sprout before being harvested. The mung bean grows on a wide range of soils but prefers well-drained loams or sandy loams, with a pH ranging from 5 to 8. It is somewhat tolerant to saline soils (Mogotsi, 2006).

Mung bean production is mainly (90%) situated in Asia: India is the largest producer with more than 50% of world production but consumes almost its entire production. China produces large amounts of mung beans, which represents 19% of its legume production. Thailand is the main exporter and its production increased by 22% per year between 1980 and 2000 (Lambrides et al., 2006). Though it is produced in many African countries, the mung bean is not a major crop there (Mogotsi, 2006).

Processes

Seed harvest

Mung bean crops grown for seeds are generally harvested when pods begin to darken. They are mostly hand-picked at weekly intervals. In newer varieties in which the plants mature uniformly, the whole plants are harvested and sun-dried before being threshed. Once pods have dried, the seeds are removed by beating or trampling (Mogotsi, 2006).

Forage harvest

The mung bean can be grazed six weeks after planting and two grazings are usually obtained (FAO, 2012). It can be used to make hay, when it should be cut as it begins to flower and then quickly dried for storage. It is possible to make hay without compromising seed harvest.

Forage management

Mung bean seed yields are about 0.4 t/ha but yields as high as 2.5 t/ha can be reached with selected varieties in Asia (AVRDC, 2012). Mung beans can be sown alone or intercropped with other crops, such as other legumes, sugarcane, maize, sorghum, fodder grasses or trees (Göhl, 1982). Intercropping can be done on a temporal basis: modern varieties ripen within 60-75 days and there is enough time to harvest another crop during the growing season. For instance, in monsoonal areas, it is possible to sow mung bean and harvest it before the monsoon season when rice is planted. It is also possible to grow mung bean on residual moisture after harvesting the rice (Mogotsi, 2006). Forage yields range from 0.64 t/ha of green matter under unfertilized conditions to about 1.8 t/ha with the addition of fertilizer (FAO, 2012)

Environmental impact

Cover crop and soil improver

The mung bean can be used as a cover crop before or after cereal crops. It makes good green manure. The mung bean is a N-fixing legume that can provide large amounts of biomass (7.16 t biomass/ha) and N to the soil (ranging from 30 to 251 kg/ha) (Hoorman et al., 2009; George et al., 1995 cited by Devendra et al., 2001; Meelu et al., 1992). Green manure should be ploughed in when the plant is in full flower (FAO, 2012).

Nutritional aspects

Nutritional attributes

Seeds

Mung beans are rich in protein (20-30% DM) and starch (over 45% DM) with a low lipid content (less than 2% DM), and variable but generally low amounts of fibre (crude fibre 6.5% DM on average). The amino acid profile of mung beans is similar to that of soybean.

Forage

Fresh mung bean forage has a moderate (13%) to high (21% DM) protein content. Like other legume straws, mung bean straw is higher in protein (9-12%) than cereal straws.

Potential constraints

Antinutritional factors

Mung beans contain several antinutritional factors (trypsin inhibitors, chymotrypsin inhibitor, tannins and lectins) (Wiryawan et al., 1997). The amounts of antinutritional factors vary greatly among mung bean types and can be reduced through processing methods such as soaking, cooking or extruding (Lambrides et al., 2006; Mogotsi, 2006; Wiryawan et al., 1997). However, in some cases, these metabolites were found to have no negative effects (Creswell, 1981).

Ruminants

Seeds

Information on the use of mung beans in ruminants is limited. Mung beans are highly fermentable in the rumen and compare favourably with coconut meal, palm meal (mechanically or solvent extracted) and dried brewer's grains (Chumpawadee et al., 2005). In a comparison of several legume seeds in the Southern Great Plains of the USA, the protein and in vitro digestible DM of mung beans indicated that they could be efficient replacements for maize or cottonseed meal in livestock diets, assuming that mung bean could generate enough grain biomass to be cost-effective. Though not as effective as soybean, the mung bean was capable of accumulating useful levels of protein and digestible dry matter under the variable growing conditions of the study (Rao et al., 2009).

Mung bean bran (chuni)

Mung bean chuni was included at 50% of the concentrates offered to buffaloes fed on a rice straw diet. It met maintenance requirements without any adverse effect on nutrient utilization (Krishna et al., 2002).

Forage

Mung bean forage sustained sheep maintenance without adverse effects (Garg et al., 2004). Mung bean straw (haulms) can be used in the same way as other cereal and legume straws. In the highlands of Afghanistan, they are mixed with rice straw and wheat straw to make a bulky component in sheep and goat diets (Fitzherbert, 2007). In a comparison of sheep and goat feeding, mung bean straw was found to be palatable to both species with no deleterious effects on animal health. Reported OM digestibilities were moderate, 56 and 61% in sheep and goats respectively (Khatik et al., 2007). DM digestibility of mung bean straw (64%) fed to ewes ad libitum was similar to that of the straws of groundnut, alfalfa and cowpea and higher than that of cajan pea straw (54%). Feeding ewes with mung bean straw increased overall DM intake from 12.6 to 18.9 g/kg LW/day (McMeniman et al., 1988).

Pigs

Seeds

Growing pigs

Mung beans are rich in protein, with a high lysine content, but the raw seeds contain antinutritional factors that may limit their use in pigs (Maxwell et al., 1989). Processed seeds have a higher digestibility in growing pigs: extrusion proved to be more effective than cooking or roasting (Canizales et al., 2009). Mung beans used as a supplementary source of lysine could be included at up to 10% in the diets of growing pigs, with weight gains similar to that obtained with maize-soybean based diets (Maxwell et al., 1989). Inclusion levels were increased up to 30% with specific cultivars (Wiryawan et al., 1997). In finishing pigs, proposed inclusion levels have been lower (6 to 9%) (Maxwell et al., 1986a), though higher rates (up to 16%) were shown to have little negative effect on performance (Maxwell et al., 1989).

Mung bean by-products

The mung bean meal, a by-product of the vermicelli manufacturing, has been tested in pig diets with satisfactory results, due to its bulk and fibre content. It could replace up to 75% of the rice bran in pig diets, with older pigs benefiting the most. Higher inclusion rates resulted in higher intakes but were detrimental to feed conversion ratio (Sitthigripong, 1996). Amino acid supplementation failed to make diets based on this product as efficient as a maize-soybean meal based diet (Sitthigripong et al., 1998).

Mung bean bran (chuni) was included at 15% level in the rations of finisher crossbred pigs (Ravi et al., 2005).

Forage

Mung bean forage has been assessed with 8 other tropical legumes as a potential alternative protein feed for pigs and ranked among the more suitable ones (Bui Huy Nhu Phuc, 2000).

Poultry

Mung bean has a higher energy value than many other legume seeds (Wiryawan et al., 1995). It is a high value resource for poultry feeds.

Broilers

High levels of mung beans have been tested in young broilers without loss of growth or feed efficiency: up to 40% mung beans in the diet gave the same performance as the maize-soybean meal based control diet. Feed efficiency was affected only when the energy level of the diet was not adjusted. There was no effect of raw mung bean on pancreas weight, and boiling mung bean did not increase performance. It can be concluded that no harmful antinutritional factors were present (Creswell, 1981).

Layers

Raw mung beans introduced at levels of 15% or 30% in the diet did not result in reduced egg production or feed efficiency. However, egg production was significantly depressed at a 45% inclusion level. Pelleting diets had no effect at the 15% or 30% inclusion rate, but had a positive effect on production at the 45% level (Robinson et al., 2001). In all cases body weight was slightly depressed by the inclusion of mung beans in the diet. The general recommendation is to use mung beans at levels up to 30% in layer diets, provided that the diet is properly balanced, especially with amino acids.

Rabbits

Little information is available in the international literature on mung bean utilization in rabbits. In a study where soybean meal was replaced by mung beans in complete feeds for growing rabbits, mung beans were introduced at up to 24% in the diet without impairing performance. The 10% reduction in growth rate observed at the 32% inclusion rate may be related to the lower protein digestibility attributed to mung beans when compared to soybean meal (73 vs. 85%) (Amber, 2000).

Fish

Asian sea bass (Lates calcarifer)

Mung beans can be used as a protein source at up to 18% in the diet of Asian sea bass without affecting growth (Eusebio et al., 2000).